A typical modern digital electronic device uses many individual self-contained functional blocks or components all of which must cooperatively interact to perform the overall function of the device. It is frequently the case that each of these functional components is assembled by interconnecting a set of integrated circuits, and the integrated circuits autonomously execute the function of that particular component. The proper functionality of the entire electronic device requires coordinated functionality from each of the functional components. Coordinated functionality is achieved by communicating data and control information between the functional components over a bus.
A parallel bus is typically used to connect those functional components which require intensive communication of data, such as a processor and memory. A parallel bus includes a relatively large number of individual conductors, for example 64, 128 or more conductors, upon which signals are simultaneously presented. The simultaneous or parallel presentation of a large number of signals on the parallel bus on a repetitive basis quickly communicates a large amount of data. On the other hand, many of the other functional components of an electronic device do not require the communication of large amounts of data on a continuous basis. It is common practice to connect such less communication-intensive components by a serial bus.
The typical serial bus involves only two conductors, one which carries a clock signal and the other which carries a data signal. The data is presented as a single signal or bit occurring during a time interval defined by the clock signal. Because only a single bit is applied at one time on the serial bus, more time is required to communicate information. However, since the typical functional components connected by the serial bus do not require a large amount of data or control information, or since the time required to communicate the data and control information is not critical, the use of the serial bus is not a particular detriment in the circumstance. In addition to its relative simplicity, the data and clock conductors of a serial bus consume less space and require a lesser number of electrical connections to the functional components, making the layout and organization of the device easier and more compact. A serial bus also makes it relatively easy to evolve electronic devices into improved versions by substituting improved functional components for the previous components while retaining the interconnection and the interaction with the other components through the serial bus.
There are many other advantages and reasons for using a serial bus, and those reasons and advantages have been endorsed by the widespread acceptance and use of serial busses in electronic devices. One type of serial bus, known by the trademark “I2C,” has been used so extensively that it has almost become the de facto standard for a serial bus. Other serial buses which have a related or similar functionality are designated by the trademarks “SMBus” and “DDC2.” Details concerning these different serial buses are described in widely-disseminated specifications published by their respectively different developers.